Advice needed for inboard motor

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Created by

Slimpro > 9 months ago, 4 Apr 2021

Slimpro

3 posts

4 Apr 2021 7:32am

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Hello Everyone
I am a new sailboat user and owner. Recently purchased a 1988 28ft mottle 820. Didn't pay a huge amount for it. Since I am a novice I employed the services of an experienced yacht owner to help me move it initially. On the initial journey under his instruction we caught the prop with rope and actually ripped the Gear box off the engine. So after being towed back the the berth I had a mechanic tell me the Gear box had some work and reattached with wrong size bolts, no biggy, so was reconnected properly. Then he said we have bigger problems, the prop shaft was bent and the engine bed was possibly rotted so the engine couldn't be fastened down tightly to the bed because the coach bolts were just spinning He quoted approx $6/7k all in, to the get the problems fixed. I got a second opinion from a former boat fibre Glasser and he suggested try drill out the engine bed mount holes inject some resin redrill and see if mountings can be fastened down. I did this and it was great success. The engine is solidly fixed to the bed now. Now, when the engines in gear and prop turning there is maybe 1mm of movement in the engine bed and also less than 1mm of movement in the rear gland where the prop-shaft exits the hull. Its done approx 5 hours and no leaks whatsover on that gland. Question is this the mechanic said I need to replace/repair engine bed and straighten prop shaft before I use the boat, to my untrained eye it looks like it is usable and I could possibly wait until the boat has to come out of the water in approx 6 months. If there is too much stress on that rear gland when they start to fail how quickly and severe do they leak? interested in your opinions, and thank you if you read all of this.

Lazzz

NSW

910 posts

4 Apr 2021 4:16pm

Have you tried turning the prop shaft when it is disconnected from the gearbox?? Does it spin nicely with no sideways movement??

Also do a Google search on aligning the motor & shaft correctly to make sure it is aligned properly.

With the 1mm movement you have suggests to me that the shaft is bent & with revs underway will do damage.

Achernar

QLD

395 posts

4 Apr 2021 5:12pm

Slimpro,

1mm sounds like a lot of movement to me. If you leave it, you could damage your seals and bearings.

I have a spare 1 inch prop shaft from my Cavalier 28 if you need it and can transport it from Brisbane. PM me if interested. I had to replace it because the taper was wrong for my new prop. I kept the old flappy-folding prop as well, but it is well off-balance and would cost nearly as much as a new prop to re-machine and re-balance (which is why I replaced it). My new shaft cost about $550. However, you'd also need to slip the boat to replace the shaft and you'd want to take the opportunity to fix up other stuff, so the cost is likely to escalate.

Ramona

NSW

7737 posts

4 Apr 2021 5:52pm

The correct answer here is depends. Is the motor bolted down hard on the bearers or is it bolted down on rubber engine mounts? Is the stern gland mounted on a rubber hose? Is there a flexible coupling between the gearbox and the shaft? Is the stern gland the packing type or a dripless unit. If you are using the motor to get on and off a mooring only I would wait the 6 months.

The best way to ask about this type of problem is with some photos which makes it all much easier.

ChopesBro

351 posts

4 Apr 2021 8:32pm

Complex. Photos would assist with advice

Slimpro

3 posts

6 Apr 2021 1:03pm

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Thanks everyone for the advice.
Here is a link to a YouTube video I uploaded with the prop shaft turning at half speed. I would say the deflection is actually less than 0.5 mm.

So back to original question is that much deflection likely to cause sudden heavy leak? It has running now approx 6 hours quite hard and no leaks whatsover.
Your advice is appreciated.

Also I know the coupling is a fixed flange not a flexible coupling.

Slimpro

3 posts

6 Apr 2021 1:27pm

Also the engine is bolted down to the engine bed on flexible mounts, the mountings themselves are solidly attached to the bed now.

Lazzz

NSW

910 posts

6 Apr 2021 6:59pm

Doesn't look too bad in the vid.

Just take it for a run & see if there is much vibration under revs - keep an eye out for leaking.

IMO it should be OK to use until you pull it out next.

Ramona

NSW

7737 posts

6 Apr 2021 7:09pm

I had trouble getting the video to run but solved that now. Has a dripless seal so that should handle some error in alignment. I would wait till your up on the slips next. Just take it easy and keep the revs down. Take the shaft out and off to a prop specialist. Watch how they straighten it. Usually one hit with a hammer!

nswsailor

NSW

1458 posts

6 Apr 2021 10:07pm

Hold it!

Have you checked the PolyFlex connector [if you have one that is] between the gearbox and the shaft.
They do work harden and can cause mechanics to make heaps of money before saying

"Oh, we had better replace the PolyFlex connector as well!'

Worth checking!

r13

NSW

1714 posts

6 Apr 2021 10:53pm

Assume you mean Polyflex coupling. They don't work harden.

www.polyflex.com.au/flexible-disc-couplings

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